1. Field of the Invention
The invention relates in general to a method of optimal power calibration. More particularly, the invention relates to a method of optimal power calibration that can derive the optimal recording power for any position of an optical storage medium such as a recordable or rewritable disk.
2. Description of the Related Art
Rewritable disks (CD-RW) and the recordable disks (CD-R) are currently popular optical storage medium in the market for data storage that a rewritable disk can vary or rewrite data stored inside, while the recordable disk can be used to record data only once. Both the rewritable and recordable disks have to undergo an optimal power calibration (OPC) process to obtain required optimal recording power before being used. FIG. 1 illustrates the operating flow of the conventional OPC process, which is basically performed on a power calibration area (PCA) of an inner track of the disk. In step 100, the recording head jumps to the count area of PCA in the inner track, while the number of recorded blocks (indicating the number of times that the OPC processes have been performed) is read for obtaining the address of the empty power calibration area in step 110. In step 120, the recording head jumps to the empty power calibration area and then starts to perform optimal power calibration process in step 130. Under OPC process, the recording head uses 15 (fifteen) different powers to write 15 frames of calibration data (or, OPC pattern) into the empty power calibration area. The recording head jumps to positions where the written operations have just performed so that the burned calibration data can be read out for determining the optimal recording power in the following steps 140, 150 and 160. The recording head then moves to the count area of the last empty PCA in step 170 and registers that one more OPC process is performed in step 180. Finally, the measured optimal recording power is used to record data onto the disk in step 190. All steps shown in FIG. 1 follow the specifications defined in Orange Book for CD-RW disks.
Conventional approaches for measuring the optimal recording power of disks are adapted to a constant linear velocity (CLV) mode rather than to a constant angular velocity (CAV) mode because the recording head follows different linear velocities for recording data in the inner and outer tracks under CAV mode. The linear velocities under CAV mode are proportional to the distances from the recording position (or, data block) to the center of the disk, while the velocities for recording the outer tracks can be as high as 2.5 times of that for recording the inner tracks. Such a difference may cause failures while recording the outer tracks by directly referring the optimal recording power derived from the power calibration area of the inner tracks. Although CLV mode is now the broadly used approach, however, it significantly consumes more recording time than that of the CAV mode. Additionally, even the CLV mode is adopted everywhere of a disk; different material coated on the inner and outer tracks should raise different requirements for recording. There is no solution now that overcomes data recording failures arisen from different material coated as aforementioned because the conventional OPC process can only find out the optimal recording power suitable for the inner tracks rather than whole the optical storage disk.